What caused North Korean leader Kim Jong Un to begin walking with a cane earlier this month? Ankle surgery, says South Korea's spy agency, as reported by Yonhap news agency on Tuesday.

Kim’s six-week absence from public events set off a frenzy of wild speculation around the world, from serious health issues to a possible coup.

The National Intelligence Service (NIS) told South Korean legislators that a foreign doctor flew to the counrty and operated on Kim in September or October to remove a cyst from his ankle, said Park Byeong-seok, an aide for opposition lawmaker Shin Kyung-min.

The NIS’s report also suggested the cyst would recur due to Kim’s health – he is obese and a heavy smoker – and his heavy public schedule, Park said the legislators were told.

Kim was last seen attending a music concert with his wife on September 3. But photos of him in public reappeared on October 14, showing Kim, using a cane, conducting a series of inspections of new residential complexes in Pyongyang.

It wasn't immediately clear how the information was obtained by the spy agency, which has a spotty track record of analyzing developments in opaque North Korea, The Associated Press reported.